Examples of such systems are described in the Applicants earlier patents Nos. 0038113, 0043660, 0059035 and 0101220 and European Application No. 0566595.
It is an object of the present invention to provide an improved form of clutch control system of the kind specified in which abusive use of the system by the operator is mitigated.
Thus according to the present invention there is provided a clutch control system of the kind specified in which the operator is warned, for example by sounding a buzzer and/or flashing a warning light, if he attempts to drive away in a designated non take-up gear or in any gear in a predetermined abusive manner.
Typically in a vehicle with a five speed gearbox an attempt to drive away in a non take-up gear is designated as an attempt to drive away in third, fourth or fifth with a vehicle speed below a predetermined level (e.g. 4 kph).
Typically an attempt to drive away in an abusive manner is defined as an attempted clutch take-up in second gear with a high engine speed (e.g. over 3500 rpm) and a low vehicle speed (e.g. below 4 kph).
Take up is also defined as abusive if it is estimated that more than a first predetermined level of energy (e.g. 40 kJ) remains dissipated in the clutch.
The control system may also be arranged to estimate the energy dissipated in the clutch in each individual clutch take-up and to warn of abuse if the energy dissipated in any individual take-up exceeds a second predetermined level (eg. 30 kJ).
The level of energy dissipated in the clutch is estimated by:
determining the clutch slip speed from the difference between engine speed and clutch driven plate speed; PA1 estimating the instantaneous torque capacity of the clutch from the position of the clutch actuator using a look-up table; PA1 determining the instantaneous power being dissipated in the clutch from the product of the slip speed and torque capacity; PA1 integrating the instantaneous power dissipated over the time period under consideration (e.g. the individual take-up or since keying on of the system) to estimate the total energy generated and PA1 subtracting periodically from this integration total an amount of energy representative of the natural cooling of the clutch to arrive at a current final total level of energy dissipated within the clutch during the time period under consideration.
In a clutch control system of the kind specified in which the level of clutch engagement is controlled by an electronic control unit in response to an engine speed error signal derived from a comparison of current engine speed and a reference speed signal generated by the control unit, said error signal being compared with a current clutch position signal to produce a clutch actuation signal, an additional control on clutch abuse is provided if an attempt is made to move away in a non take-up gear by not allowing the reference signal to increase above a predetermined level (e.g. 1100 rpm), or reducing the reference signal, as the throttle is opened. This containment of the reference signal may be extended to take-up in second gear, if desired. By not increasing the reference signal this ensures a more rapid clutch engagement thus reducing energy generation in the clutch.
In an alternative configuration the system may be configured to rapidly disengage the clutch to prevent the dissipation of excessive energy in the clutch. This rapid disengagment may be achieved by rapidly raising the value of the reference signal.